A whale's consumption of squid

Okay, I do not know where my copy of Search for the Giant Squid is, so this information may be (and probably is) problematic.

As far as I know, the weight of squid consumed by the sperm whale population equals or exceeds the weight of the human race. And according to logic, some prey must be able to escape. Allow me to extrapolate: the population of squid, giant and otherwise, is much larger than many people can comprehend.

The math all depends on how many squid the whale eats each day, and how long the beaks remain in the stomach (prior to being regurgitated - if in fact all beaks are regurgitated). It also depends on our equations for determining squid size based on beak size, and for a number of these deep-sea species of squid we know very little about them (and the conversion equations are not correct).

One of the things that never ceases to amaze me is that during all deployments of crittercams to whales NOT ONE squid (to the best of my knowledge) has been seen being eaten (giant or otherwise). If the male sperm whale eats 350+ squid per day, and the female 700+ per day, just to sustain its bulk, then you would expect to have seen at least one squid being chomped. [even though the bitey end of the whale is a very long way from the camera end at the top]

If you think about it too hard you'll get a sore head. The male eats less squid per day but attains larger size? That's odd. Maybe it eats larger squid (so doesn't need to eat as many smaller squid). Questions, questions, questions ....

Another one of those weird facts is that the whale is eating species of squid that are generally considered to be extremely rare (even in massive fishing trawls .... those nasty 'bottom trawls' that destroy the seabed and catch everything in their path). So, how is the whale catching them - are the squid really that good at escaping nets (some things like Architeuthis, Pholidoteuthis, Mastigoteuthis and Histioteuthis are regularly caught my trawl .... but I could count on one hand the number of Lepidoteuthis, 'giant' Octopoteuthis and Gonatus that exist in NZ marine collections, and these brutes seem to be consumed in great numbers by the whale). Mesonychoteuthis is not known from NZ waters (one specimen is known a stone's throw south of South Island) - so many of these fresh-looking beaks that are recovered from the stomachs of these whales have probably been eaten in waters outside of the New Zealand EEZ .... and there's no way that a whale is swiming at supersonic speed to get from ~ Antarctica to northern New Zealand in 2 days (this is how often they think the whale regurgitates the contents of its stomach [beaks]). So, I think there are a few flaws in the math ...

The squid will still be super-abundant, but not as abundant as some estimates have stated.

One passage in particular:
With regard to how long the beaks remain in the stomach (Clarke 1980: 52, 53):
'If the average whale eats 10 meals a day it would consume 330 squids a day and the average number of beaks in the stomach [1300] would represent 4 days food. This figure, for both sexes combined, is not very different from a direct calculation of the average rate at which beaks are accumulated in whale's stomachs estimated from their food requirements [between 700-800 squids per day for the average female and 300-400 for the average male]. Dividing these figures into the average number of lower beaks recovered from sperm whale stomachs shows the average female retains the beaks for 2.1-2.5 days and the average male for 1.2-1.6 days' [slightly paraphrased].

Of particular interest is that the average number of beaks in the stomachs of these stranded specimens is nowhere near 1300! However, there is a major difference between the two sources of samples, with Clarke's stomachs recovered from harpooned whales and ours from stranded specimens. It is not possible to know whether any were regurgitated (to account for the reduced numbers) [but likewise for Clarke's specimens].

I have never seen squid beaks littering the beach drift after any of these strandings (as in it wouldn't appear that beaks were regurgitated whilst the animals were thrashing/dying on the beach - it's a very sad thing, but a fact of life). If I had I'd definitely say that stomach contents were at least partially regurgitated.

I'll need to complete lower beak identifications (and counts) on all whales before I can calculate averages (and deviations); the 1300 figure cited by Clarke is for lower beaks only (I would assume).

How do the Mesonychoteuthis beaks you have recovered in this, and other, sperm whales compare to the intact specimen you examined recently in size? Are the whales catching older more mature specimens on average, or are they predominantly feeding on juveniles? Also, and I apologise for a biggie, has the average size of recovered beaks altered in the last few years, with implications as to alterations in both whale and squid migration patterns?

Click to expand...

You've hit the nail on the head Phil. There are two big questions that I want addressed re squid in the diet of toothed whales:
Is the composition changing over time?
Is the size-class frequency distribution changing over time?

Click to expand...

And ... from this a third question has developed (I like the way this has developed).

3) Is there a change in the number of squid the whale is consuming on a daily basis?

Perhaps the whale is rather selective in what it eats, and the number of squid consumed reflects their abundance. I'd not thought to compare 'historical average number of squid consumed' on a daily basis with present-day consumption rates (thinking the most obvious difference would have been reflected in species composition and size-class frequency distribution).

Adverse environmental conditions, insufficient nutrition, and chronic stress from disturbance or competition can act through the pituitary-adrenal axis to suppress the immune response, so that otherwise benign flora can become pathogens. For example, in sea lions the prevalence of some organisms may be a reflection of the stresses of coping in a sub-optimal environment rather than of the virulence of the bacteria. Similarly, in fur seals stresses may be imposed in La Niña summers when food resources appear to be scarce and most of the animals presented for examination are malnourished. For stranded individuals of other species, too little information is available to assess what external factors may have affected the health status of individuals.
..............

We are presently looking at the stomach contents of the 'other species' (strandings)

Just something I thought of last night... Accounts of Sperm Whale stomach contents taken from 'harvested' whales, record bits of partially digested squid and in some cases whole squid. The whale stomachs I've seen have had only beaks. This (to me at least) suggests that these stranded whales had not eaten in a while. Which again, rasies more questions...

Is there any possibility that when the whale regurgitates its stomach contents, beaks, being heavier or denser or whatever, are retained? And could thus represent months or years worth of eating, instead of days?

It just seems bizarre that the whales have this many beaks in stomach but that whale cams do not record the whales eating a single squid. Also that Antarctic whales could jet up to the temperate zone within a few days.

.... what we have to do is get a giant squid carcass, insert a camera or temperature probe into it, take it to a whale, hopefully the whale will eat it, then track the path of the camera/probe through the whale.

I'm dead serious!!

We'd sure find out how often the whale regurgitated if we did this! Myopsida's pics of a whale taking a fish at the surface in Kaikoura are proof that the animal does/can feed at the surface.